The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head traditionally includes a coil layer embedded in one or more insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air hearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In current read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor has been employed for sensing magnetic fields from the rotating magnetic disk. A GMR sensor includes a nonmagnetic conductive layer, referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering after the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
Other magnetoresistive sensors that can be used in a magnetic write head are tunnel junction sensors, also referred to as tunnel valves, and current perpendicular to plane giant magnetoresistive (CPP GMR) sensors. Extraordinary magnetoresistive sensors have been proposed as well for use in magnetic data recording heads.
Regardless of the type of magnetoresistive sensor used in a magnetic head, a challenge that affects the manufacturability of magnetic heads is the problem of Electrostatic Discharge (ESD). Recording heads can be ruined or badly degraded by stray electrostatic discharge events. Although a variety of solutions have been proposed for preventing electrostatic discharge in a write head, no practical solutions are available that can be employed after slider lapping.
As those skilled in the art will appreciate, sliders having magnetic read/write heads are constructed by a process wherein thousands of read/write heads are constructed on a wafer. This wafer is then sliced into rows. The rows of sliders are lapped to remove a desired amount of material from the cut edge of the row of slider, thereby defining the stripe height of the sensor and forming an air bearing surface on the slider. These rows are later cut into individual sliders.
Previously proposed solutions for preventing electrostatic discharge in a magnetic head have included providing some sort of electrical shunt structure that is removed prior to cutting the wafer into individual sliders. The shunt structure must be removed in order to test the slider (e.g. quasi test) and in order for the sensor to function in the finished disk drive. However, there remains a large risk of ESD damage after testing has been completed, before the slider has been assembled into a finished head gimbal assembly and suspension assembly. To make matters worse, the need for ESD protection is becoming more pronounced with each evolution in the sensitivity of the sensor.
Therefore, there is a strong felt need for a method or structure that can prevent electrostatic discharge (ESD) from damaging a magnetoresistive sensor at various stages of manufacture, even after testing has been completed.